VERFAHREN ZUR HERSTELLUNG VON BIS-BENZAZOLYL VERBINDUNGEN

The present invention provides a process for the preparation of a compound of the formula wherein Y represents -O-, -S- or -N(R2)-, R2 being hydrogen, C1-C10alkyl or aralkyl; Z represents a 2,5-furanyl, 2,5-thiophenyl, 4,4'-stilbenyl or a 1,2-ethylenyl residue and R1 represents hydrogen, halogen, C1-C10alkyl, C1-C10alkoxyl, cyano, COOM or SO3M, M being hydrogen or an alkaline or alkaline earth metal, characterized by reacting a compound of the formula with a dicarboxylic acid of the formula HOOC-Z-COOH (3) or an ester thereof, Y, Z and R1 being as previously defined, in N-methylpyrrolidone or N,N-dimethylacetamide, in the presence of an acidic catalyst and, optionally, in the presence of a secondary solvent capable of removing water from the reaction mixture, which are useful as optical whitening agents for natural and synthetic materials.